The invention relates to a fuel filter, in particular for operation of internal combustion engines of vehicles.
Fuel filters for filtering fuels that operate with pressure action or suction action are known. The fuel filters prevent contaminants that are contained in the fuel from reaching the internal combustion engine. The fuel contains finely dispersed or dissolved air. When operating the fuel filter with suction action, the air is outgased from the fuel. This air collects within the fuel filter at the unfiltered side. Since the air does not pass through the filter medium of the fuel filter, the liquid level in the fuel filter will drop so that the available effective filter surface area is significantly reduced. Moreover, the drop of the liquid level means that only a portion of the filter surface area is utilized for filtration and water separation instead of the entire filter element. For water separation, however, a certain filter surface area that depends on the flow rate is required. When the filter surface area drops below this value because of the dropping liquid level, the water separation action will deteriorate to an unsatisfactory level. Moreover, at the same time, the flow velocity in the filter medium will increase which is disadvantageous for the filtration process. At the same time, the pressure differential between the unfiltered side and the filtered side will increase.
For preventing air from collecting at the unfiltered side different devices, for example, air bores or flow passages have been used. However, in particular in the case of openings provided for air there is the disadvantage that unfiltered fuel can also reach the filtered side.